bug#66948: [PATCH] Add Completion Preview mode

[Eshel Yaron]

Juri Linkov <juri@linkov.net> writes:

>> If you try it out and have any other suggestions, please let me know.
>> Here's the updated patch:
>
> Thanks, everything works nicely now.
>

Great.

> Only one thing that I suggest is to add `backward-delete-char-untabify`
> to `completion-preview-commands` since it's bound to DEL in Lisp buffers.
> Or there is no way to generalize it for all modes?

I too wonder if there's a good generalization we can make here.  It
seems impractical and inelegant to track all backward-deleting commands
in `completion-preview-commands`.  We could try to check if a command
was invoked by pressing DEL, regardless of what command it actually is,
but I don't think that's such a good solution because of course the DEL
key itself is not the point--we want to recognize `delete-backward-char`
even if it's bound to some other key, for example.

The current solution, of providing a minimal list of commands in
`completion-preview-commands`, basically delegates the decision of which
further commands should keep the preview alive to major mode authors and
to the users themselves.  I think that's basically fine, but if we had
some way to recognize backward-deleting commands without hard-coding
them (perhaps a symbol property such as `delete-backward-command`) that
would be even better IMO.

> For example, in c-mode DEL is bound to `c-electric-backspace`, etc.

Yes, and there's also Org mode's `org-delete-backward-char` and
certainly a couple more...